1. Field of the Invention
This invention relates generally to the fields of molecular biology and molecular medicine and more specifically to the identification of proteins involved in programmed cell death, cytokine processing and receptor signal transduction, and associations of these proteins.
2. Background Information
Programmed cell death is a physiologic process that ensures homeostasis is maintained between cell production and cell turnover in essentially all self-renewing tissues. In many cases, characteristic morphological changes, termed “apoptosis,” occur in a dying cell. Since similar changes occur in different types of dying cells, cell death appears to proceed through a common pathway in different cell types.
In addition to maintaining tissue homeostasis, apoptosis also occurs in response to a variety of external stimuli, including growth factor deprivation, alterations in calcium levels, free-radicals, cytotoxic lymphokines, infection by some viruses, radiation and most chemotherapeutic agents. Thus, apoptosis is an inducible event that likely is subject to similar mechanisms of regulation as occur, for example, in a metabolic pathway. In this regard, dysregulation of apoptosis also can occur and is observed, for example, in some types of cancer cells, which survive for a longer time than corresponding normal cells, and in neurodegenerative diseases where neurons die prematurely. In viral infections, induction of apoptosis can figure prominently in the pathophysiology of the disease process, because immune-based for eradication of viral infections depend on elimination of virus-producing host cells by immune cell attack resulting in apoptosis.
Some of the proteins involved in programmed cell death have been identified and associations among some of these proteins have been described. However, additional apoptosis regulating proteins remain to be found and the mechanisms by which these proteins mediate their activity remains to be elucidated. The identification of the proteins involved in cell death and an understanding of the associations between these proteins can provide a means for manipulating the process of apoptosis in a cell and, therefore, selectively regulating the relative lifespan of a cell or its relative resistance to cell death stimuli.
The principal effectors of apoptosis are a family of intracellular proteases known as Caspases, representing an abbreviation for Cysteine Aspartyl Proteases. Caspases are found as inactive zymogens in essentially all animal cells. During apoptosis, the caspases are activated by proteolytic processing at specific aspartic acid residues, resulting in the production of subunits that assemble into an active protease typically consisting of a heterotetramer containing two large and two small subunits. The phenomenon of apoptosis is produced directly or indirectly by the activation of caspases in cells, resulting in the proteolytic cleavage of specific substrate proteins. Moreover, in many cases, caspases can cleave and activate themselves and each other, creating cascades of protease activation and mechanisms for “auto”-activation. Thus, knowledge about the proteins that interact with and regulate caspases is important for devising strategies for manipulating cell life and death in therapeutically useful ways. In addition, because capsases can also participate in cytokine activation and other processes, knowledge about the proteins that interact with caspases can be important for manipulating immune responses and other biochemical processes in useful ways.
One of the mechanisms for regulating caspase activation involves protein-protein interactions mediated by a family of protein domains known as caspase recruitment domains (CARDs). The identification of proteins that contain CARD domains and the elucidation of the proteins with which they interact, therefore, can form the basis for strategies designed to alter apoptosis, cytokine production, cytokine receptor signaling, and other cellular processes.
Thus, a need exists to identify proteins that contain CARD domains. The present invention satisfies this need and provides additional advantages as well.